Recommended for grades 3-4
Key Elements of Lesson 7:
- The “water cycle” is the way that water moves through a natural system — from the ocean, to clouds, to rain, directly to streams or to groundwater then to streams, and back to the ocean.
- The water cycle is powered by the sun.
- The ocean is the cycle’s reservoir.
- Groundwater is an important, unseen mover of water.
Outcomes of Lesson 7:
- Students will be able to demonstrate an understanding of how water is our most recycled resource on earth.
- Set up a standard distillation apparatus in which students can observe evaporation and condensation of water.
Water: The Constant Traveler
(Portions of this lesson and associated activities were adapted from The Stream Scene: Watersheds, Wildlife and People by Patty (Farthing) Bowers et al, Oregon Department of Fish and Wildlife, 1990, Washington Department of Fish and Wildlife Outreach &. Education.)
Overview of the Water Cycle
Everything that grows needs water. Water covers about three-quarters of the earth’s surface. Of this, only a small amount is fresh water and less than one-third of all fresh water is usable by humans. The rest is locked in shrinking polar ice caps and glaciers — the affect of changing climate. Water is continually recycled and transported by the water cycle, over and over again. The water cycle is also called the “hydrologic cycle.”
The energy to drive this cycle comes from the sun. Water is moved into the atmosphere through evaporation and plant transpiration. When water evaporates into the atsmosphere, impurities in the water are, in fact, left behind. Evaporation is a purifier. The atmospheric vapor created by evaporation is transported by wind and condensed (concentrated) into clouds, then returned to earth as precipitation (rain, snow or hail). It is estimated that every nine to 12 days, all moisture in the atmosphere falls to earth. This means that water is our most recycled resource.
While the water cycle transports and purifies water, its effectiveness can be negatively affected by:
- Loss of vegetation – which reduces the amount of plant transpiration, and
- Atmospheric pollution – which adds contaminants to otherwise pure water vapor.
Here in Washington state
Moisture-laden clouds that developed over the Pacific Ocean move inland. As clouds rise over the Olympic Mountains, their water vapor cools, causing water to condense into drops, and it falls to earth as rain. This is called precipitation, and it continues as the clouds move east, dropping more moisture to earth as they rise over the Cascade Range. The Cascades intercept most of the precipitation, and as the clouds reach the other side of the range, they no longer rise into cooler air. Rainfall drops dramatically in the flat areas of the state east of the Cascades, and does not pick up again until the clouds reach mountains on the eastern side of the state. The result is a rain-shadow effect in Eastern Washington. It is much more arid than the western part of the state.
The short reading and questions are designed to be performed by students on their own, as preliminary work for discussion and following lessons. However, students will benefit from working on it together in small groups or as a class. The water cycle diagrams could also be completed in groups or individually. DO WE HAVE THE NECESSARY DIAGRAMS???
- Water in the ocean is heated by the sun. When the water has taken in enough energy (heat), it will evaporate and rise into the air (just like heating it in a pan). As it rises, the water cools, condenses, and turns into clouds. When the clouds hold enough water, it will probably rain or snow.
Student Reading: Water – The Constant Traveler
Have you ever seen the ocean? It’s so big, you can’t think about it with just one thought. It takes lots of thoughts to take it all in.
Sarah and her little brother Mario saw the ocean for the first time today. After looking at it for a long time, Mario said, “Where does all the water come from? It must take a lot to fill it up!”
“It must come from rivers and streams.” answered Sarah.
“And where does the water come from to fill the rivers and streams?” replied Mario. “Oh, from rain!” he said, before Sarah could answer. “And snow too,” Sarah
“O.K. What about the rain and snow? The water to make them falls from the sky. Where does that water come from?”
This was a harder question. They both looked up at the bright, white fluffy clouds and blue sky.
“When it rains,” reasoned Mario,” the rain seems to come from the clouds. But there are clouds now, and it isn’t raining. So, only some clouds have water in them.”
“Rain clouds are darker ~ sort of gray and dark blue,” replied Sarah, still thinking about where the water for rain and snow comes from. “I think the clouds ARE water. Just like fog. And when there’s enough water in the clouds, it rains. Or if it’s cold enough, it snows.”
“Where does the water come from to make clouds?” questioned Mario. Sarah was getting a little tired of answering her brother’s questions, so her answer was a little sharp.
“From the sun!” She really didn’t know the answer either. Do you?
1. You can help Mario and Sarah solve the mystery of the water cycle. Here’s how:
- Using the drawing below, draw arrows from the place the water comes from to the place it goes. Use the previous story for clues. Then, try to figure out where the water comes from that makes clouds.
- HINT: Have you ever seen steam rising over a pan of boiling water? The heat from the stove burner heats the water until steam is produced. The water would all be turned into steam if it were heated for a long time. The steam goes into the air. Now, think back about the big ocean. Is anything heating it up? If water gets enough energy, it does a surprising thing. Fill in the blanks below:
2. Water in the ocean is heated by the _____.
3. When the water has taken in enough energy, it will _______ and rise into the _______.
4. As it rises, the water cools, condenses, and turns into _______.
5. When the clouds hold enough water, it will probably _______ or _______ .
Draw the water cycle diagram in your journal and use arrows of different colors to show evaporation, transpiration and precipitation.
Diagram: The Water Cycle
(Click to expand.)
You have drawn what is called a WATER CYCLE, and it’s the way water gets around on our earth. All water, from the big ocean, to clouds, to rain and snow, to creeks, streams and rivers, and underground water (the water that we get from wells) is connected by the water cycle. The ocean is really a big reservoir for this water cycle, because about 98 percent of all the water on the earth is in the oceans! The rest is fresh water, in streams and rivers, or locked up in polar ice caps and glaciers.
But there’s a little more to this water cycle. All plants give off water as a gas (called transpiration). This is another way that water finds its way back into the sky to make clouds. And, most kinds of soil and rock can hold some water. We call this ground water, and it’s the water we tap into when we drill a well. This water eventually ends up in streams and rivers, and on its way to the ocean.
Make two more arrows on your water cycle diagram to show how transpiration and ground water fit into the water cycle. Don’t forget to color the thing that powers the water cycle on your diagram. If you can’t remember what that is, review your work above!